The present invention relates to a discharge lamp control device and a projector.
A discharge lamp such as a high-pressure mercury lamp or a metal halide lamp is used as a light source of a projector. When lighting a discharge lamp, a high voltage of several tens of kilovolts is normally generated between electrodes of the discharge lamp in order to cause a dielectric breakdown between the electrodes of the discharge lamp to form a discharge path. The voltage (discharge lamp voltage) between the electrodes of the discharge lamp rapidly decreases immediately after the discharge lamp has been lighted. In order to heat the electrodes of the discharge lamp so that the discharge lamp voltage increases to a value near the rated voltage value, constant current control is performed so that a discharge lamp current which flows between the electrodes of the discharge lamp becomes constant when the discharge lamp voltage is lower than a predetermined voltage value. When the discharge lamp voltage has become equal to or higher than the predetermined voltage value, constant power control is performed so that the amount of power supplied to the discharge lamp becomes constant. According to a related-art method, as shown in FIG. 7A, a discharge lamp current near the maximum design current value of the discharge lamp is caused to flow during constant current control in order to reduce the transition time from constant current control to constant power control. In a discharge lamp lighting device disclosed in JP-A-9-82480, for example, the discharge lamp current during constant current control is set to be higher than the discharge lamp current during constant power control.
However, the electrodes of the discharge lamp may be melted due to the high discharge lamp current during constant current control. The discharge lamp current during constant current control may be limited to prevent such a problem. However, since the discharge lamp is turned off if the discharge lamp current is limited to a large extent, the discharge lamp current cannot be reduced to a large extent.
In order to extend the life of the discharge lamp, the discharge lamp may be driven by applying an alternating current so that a current evenly flows between the electrodes of the discharge lamp. According to a related-art method, the drive frequency is set at a constant frequency, as shown in FIG. 7B. However, the electrodes of the discharge lamp are easily damaged due to a large change in current when the polarity of the discharge lamp current changes. Therefore, the electrodes of the discharge lamp deteriorate when the drive frequency is too high, whereby the life of the discharge lamp decreases.